Questions about wall construction / new single-family house (solid)

Hello dear forum,

we are currently planning the construction of a solid single-family house with the following basic data:

[*]Plot: 417sqm
[*]Living space: approx. 155sqm
[*]Min. KfW 70 standard
[*]Heating technology: air-water heat pump (reasons: gas connection is not possible, gas tank rather not desired / geothermal energy via surface collectors is probably excluded due to the plot size / geothermal drilling possibly not possible because of thermal spring protection area
[*]Federal state: Hesse

One question has been worrying us for quite some time now, namely that of the wall structure. It is clear to us that there is no perfect stone/wall structure and that every building material has its own advantages and disadvantages. That is exactly why the decision is so difficult for us.

I would like to apologize in advance for any overly general or factually incorrect statements. We are truly not experts in this field and appreciate every food for thought .

The following points are important to us (probably like for everyone):
- Healthy indoor climate
- Good insulation values and as low heating costs as possible (future-oriented)
- Good sound insulation
- Good behavior with moisture/low susceptibility to mold

At the moment we favor Poroton. The properties of the brick sound reasonable to us and Poroton is widely used in our area. In addition, this construction method is offered as a standard by many regional construction companies. But here it already starts. Often, a 17.5 cm brick + 16 cm solid thermal insulation composite system (ETICS) (e.g. rigid foam insulation boards or mineral wool) is planned as standard, since this combination is supposedly the easiest/cheapest way to achieve the KfW standard. After long research (also here in the forum), we are still not sure whether this construction method is advantageous compared to a monolithic one or not. On the one hand, you hear about the good properties of ETICS such as lower risk of thermal bridges but also about the less favorable properties (worse indoor climate etc.).
Intuitively, we tend to a monolithic masonry wall with a 36.5 cm thick hollow brick (T8 or T9) without additional insulation. We expect better indoor climate and better moisture protection from this (as mentioned, this may be a generalized misjudgment ).
KfW 70 standard can be achieved with both construction methods in combination with an air-water heat pump.

My specific questions are:

[*]Which wall structure is better suited for a new building or more future-oriented? Suitable alternatives to those described above are of course also welcome.
[*]If one decides on an ETICS, which material is more recommendable here (I often read about polystyrene or mineral wool)?
[*]With which structure are better insulation values achieved (I assume with additional insulation)?
[*]Which construction method is more prone to building defects and/or mold formation?
[*]Should one generally consider a central/decentral ventilation system in a new building? Since we both work full-time all day, longer and especially regular airing by shock ventilation is rather difficult or tends to be neglected after some time. If avoidable, we would also like to do without additional technical gadgets (high acquisition costs and regular maintenance). Regarding this point, I would like to mention that we have received very different opinions from various construction companies. Some are of the opinion/claim that a monolithic construction is clearly advantageous with regard to moisture/air exchange and that an additional ventilation system is not necessary. But this seems somewhat too simple to me, since the often-cited “breathing wall” does not exist. Other builders solve this with a decentralized ventilation system or with ventilation slots in the windows (which are only installed after the blower door test – does it even make sense to check airtightness first and then install ventilation slots?).

For your suggestions, I would like to thank you very much in advance!!

Exactly this discussion can be found and is currently in full swing

... of course, it’s all a question of cost ...

Hello,

you are really facing a difficult decision right now. We will also build with Poroton T8 or T7. I see thermal insulation more as an option for retrofitting old buildings and personally, I do not find it necessary, at least with Poroton. I prefer to take a thicker, continuous brick right away. We hope for a better indoor climate and better thermal insulation in summer! And personally, I just don’t like the thought of having plastic/styrofoam on the walls right from the start again... By the way, there is also insulation made from wood wool.... Edit: If you now build completely solid, there is still the possibility later to add insulation on the outside if standards were to change drastically. Just like is done nowadays with old buildings.

Regarding the different types of bricks, I can recommend the posts by Bauexperte in this thread:

And on the topic of controlled residential ventilation, there are the following threads. We have not yet made a final decision as to whether and if so, what type. If we do, it will probably be a decentralized ventilation system, simply because you don’t have long “hoses” that could potentially become a hygiene problem.

I personally find ventilation slots at the windows stupid... Where is anything controlled there? It just drafts. Just like in the old days with old windows, where the wind whistles through in front and back...

Thank you very much for the answers!

: Are the T7 and T8 you mentioned filled bricks? There are countless different opinions on this topic as well. The question is whether the difference to a wall with an uninsulated 36.5 cm hollow brick is really that significant. There is also a considerable cost difference here. However, I naturally want to avoid building a new house today (in this example with a 36.5 cm plan brick) that will already require energetic renovation in a few years - KfW 70 or not...

Regarding ventilation: From a cost/benefit perspective, a decentralized ventilation system would probably be the only option for us. I think we should do something, as no one will be in the house between 7 a.m. and 6 p.m.

The T7 is only available filled and the T8 is available filled or unfilled. (Whereby we will probably use the W08 or W07 from Leipfinger-Bader and not from Schlagmann, but they are almost the same, only the filling differs) Whether filled or unfilled is irrelevant for the U-value according to the brochure. Only the sound insulation changes between the filled and unfilled. However, I cannot say anything about that in practice...

So in the north, the brick is now also present... people often build double-shell walls with insulation - even in new construction. There are now also numerous insulation options... from polyurethane to flax or sheep wool - so from eco-comfort materials to off-gassing chemicals.